Fe 2+ /Fe 3+ Cycling for Coupling Self-Powered Hydrogen Evolution and Preparation of Electrode Catalysts.

A novel Zn-Fe flow battery featuring an Fe 3+ reduction reaction (Fe 3+ RR)-coupled zinc oxidation, and an Fe 2+ oxidation reaction (Fe 2+ OR)-coupled hydrogen evolution reaction (HER) system as well, was established. This battery is capable of driving two Fe 2+ OR-coupled HER systems in series based on the above Fe 2+ /Fe 3+ cycling, for efficient self-powered hydrogen evolution. Meanwhile, this Fe 2+ /Fe 3+ cycling enables the preparation of a multifunctional catalyst, Pt-3@SXNS (siloxene nanosheet), by the Fe 2+ OR-promoted dispersion of Pt nanoparticles on SXNS; alternatively, this support could be obtained by Fe 3+ RR-assisted exfoliation using Fe 3+ from the anolyte of Fe 2+ OR-coupled HER. The Pt-3@SXNS catalyst exhibits excellent catalytic activities toward Fe 3+ RR in the Zn-Fe flow battery, HER, and Fe 2+ OR in the electrolyzer, which is attributed to the strong electronic interaction between Pt and Si. This work offers a new strategy for energy storage and low-cost hydrogen production from acidic wastewater.